We propose to conduct a planning grant (R34) in which we will develop specific procedures, protocols, and assessments fora clinical trial evaluating the impact of coenzyme Q10 (Q10) on aging. The aims of the planning grant include generation of protocols and flow sheets for recruitment, laboratory management, quality control, data management and data sharing; finalization of the protocol and report forms; pilot testing for feasibility and acceptability of trial elements, then of the full protocol on age-relevant subjects; and development of the Manual of Operations. We propose to use these products to conduct a randomized, double blind, placebo-controlled trial to assess the impact of Q10 on outcomes germane to aging, including quality of life (QOL) (primary). We will leverage the substantial costs of conducting a RCT by secondarily addressing specific elements that are affected in aging and contribute to QOL, and for which there is preliminary support for benefit by Q10. These include muscle function, energy, cognitive function, pain, activity and sleep. We will further assess how measures of mitochondrial (mt) function relate to aging outcomes; and how Q10 affects these measures. Changes in mt function are increasingly viewed as a critical part of the aging process. Furthermore, Q10 is increasingly used as a supplement to protect against elements of aging. Q10 is a pivotall mitochondiral nutrient that serves key respiratory chain, redox, antioxidant, and antiapoptic function. It increases levels of other antioxidant nutrients; bypasses respiratory chain enzyme defects; and increases mt number. It has been reported to provide clinical benefits of relevance to aging and QOL including improvement in energy, exercise tolerance, blood pressure and glucose tolerance; and protection against arrhythmia, heart failure, and neurodegenerative disease. Thus there is strong conceptual as well as clinical rationale for assessing whether Q10 provides QOL & functional benefits in aging and whether it protects against untoward events associated with age.